Cellular binding of benzo(a)pyrene to DNA characterized by low temperature fluorescence

A new approach has been developed to detect ultra low concentrations of benzo(a)pyrene products bound to nucleic acids $\text{in}\text{vivo}$. The binding to DNA of hamster embryo cell cultures was characterized by low temperature fluorescence spectroscopy. The method can detect less than one polycyclic hydrocarbon residue per 50,000 nucleotides. The fluorescence spectra indicate that the benzo(a)pyrene derivative bound to DNA has a pyrene-like chromophore and resembles that obtained when DNA is reacted $\text{in}\text{vitro}$ with the 7,8-diol-9,10-oxide of benzo(a)pyrene. This confirms that metabolism of the 7,8,9,10 ring on benzo(a)pyrene precedes reaction with DNA. The method should be useful for detecting and characterizing the $\text{in}\text{vivo}$ binding of other fluorescent carcinogens to nucleic acids.